The present invention relates to machines, and, in particular, relates to micromachines, and further, relates to free-standing microtube devices.
In recent years there has been tremendous interest in miniaturization due to the high payoff involved. One area of current interest is microelectromechanical systems (MEMS) and the closely related fields of micro-fluidics and micro-optical systems. Presently, these technologies involve micro-machining on a silicon chip to produce numerous types of devices, such as sensors, detectors, gears, engines, actuators, valves, pumps, motors, and mirrors on the micron scale. The first commercial product to arise from MEMS was the accelerometer manufactured as a sensor for air-bag actuation. On the market today, there are also micro-fluidic devices, mechanical resonators, biosensors for glucose, and disposable blood pressure sensors that are inserted into the body.
The vast majority of microsystems are made almost exclusively on planar surfaces using technology developed to fabricate integrated circuits. That is, the fabrication of these devices takes place on a wafer and the device is formed layer-by-layer with standard clean-room techniques that include e-beam or photolithography, thin-film deposition, and wet or dry etching.
Although there have been numerous and very innovative successes using these silicon wafer-based technologies, there are some disadvantages. Since it requires the building-up of many layers of different materials as well as surface and bulk micro-machining there are some very difficult material science problems to solve. These include differential etching and laying down one material without damaging a previous layer. In addition, there are the problems associated with interconnecting layers in a chip with different functions. An example of this would be a micro-fluidic device in which there are both fluidic and electronic functions. Clearly, there are numerous materials"" issues central to this technology.
In addition to these processing problems, there are other limitations inherently associated with conventional lithographic techniques that are based on planar silicon. For example, in some applications such as those that involve surface tension in fluidics, it is important to have a circular cross-section. However, it is impossible to make a perfectly round tube or channel on a chip with current technology. Instead channels are made by etching a trench and then covering the trench with a plate. This process can only produce angled channels such as those with a square, rectangular, or triangular cross-section.
Thus, there exists a need for microtube devices not associated with planar technology.
In the present invention, a technique is described for manufacturing microtube devices which have interior geometries that are not uniform along the tube or device axis. These geometries may exist at only one location along the axis of the microtube device or specific geometries may be repeated either uniformly or non-uniformly with micron or sub-micron precision along the tube or device axis. The preferred manufacturing process involves first forming a complex fiber mandrel. {In this application we define a complex fiber mandrel as one that can not be formed by extrusion, pultrusion, spinning, stretching, or drawing (with or without a die) under uniform fabrication conditions that do not vary with time.} Once the complex fiber mandrel has been formed, it is given at least one metallic and/or nonmetallic coating by any of a variety of techniques. The complex fiber mandrel can then be removed by appropriate chemical or physical means that do not adversely affect the coating(s) desired for the tube wall. This results in a microtube structure having an interior axial profile duplicating the exterior profile on the mandrel from which it was formed. The microtube structures of this application as well as the microtubes and microtube devices of previous patents can stand alone or can be a component part of another device.
One group of techniques for forming a complex mandrel consists of employing non-uniform conditions while making fibers using techniques normally employed in the production of fibers. Another group of techniques for forming the complex mandrel consists of adding material to, removing material from, or redistributing material on a fiber core at precise locations on the periphery of the fiber core, which consists of one or more fibers held rigid during processing. The term fiber as used here is used in its most general sense and refers to natural or synthetic filaments of any material such as polymer, cellulose, glass, ceramic or metal. In the case of material addition to the fiber core, the added material may be of the same composition as the fiber core or of a different composition. An additional type of technique for forming a complex mandrel involves wrapping at least one threadlike component around a core. These overwrap threadlike components may be of the same composition as the core or they may be of a different composition. In the simplest example both the core and the overwrapped threadlike component are as-extruded or as-drawn fibers. However, it should be noted that in some applications the core can also be a macroscopic object with a threadlike component, microtube, or microtube device wrapped around it.
To form a complex mandrel by the wrapping of one fiber around another involves drawing a single core fiber (or bundle of core fibers) through a confining orifice. The overall fiber core is held with minimal constraint (typically by friction), so that no breakage takes place as it is drawn through the orifice. However, enough constraint exists so that torque applied tangentially by an overwrapping fiber (or fibers) as it is being wound around the fiber core does not cause the one or more core fibers to slip in the direction of applied torque. Moreover, the overwrapping one or more fibers must be wound sufficiently close to the constraining orifice that twisting of the core one or more fibers in the direction of torque is minimized to such an extent that unwinding, or xe2x80x9cbacklashxe2x80x9d does not occur when constraining forces are removed at the end of winding. Also, sufficient force must be exerted by the overwrapping fiber to insure that it winds itself tightly around the fiber core, thereby precisely maintaining desired dimensions and geometry. Finally, physical properties of the overwrapping fiber must be such that torsional stresses remaining after winding are insufficient to disrupt configuration of the formed mandrel when constraining forces of the winder are released. Polyetherimide has been found to be an excellent overwrapping fiber in this respect.
Therefore, one object of the present invention is to provide several methods for making complex fiber mandrels.
Another object of the present invention is to provide a precision-controlled adjustable-torque micro-winder able to wind one or more micron-sized fibers around a core of a micro-object, macro-object, or at least one micro-sized fiber.
Another object of the present invention is to provide a method of making microtube devices from complex mandrels.
Another object of the present invention is to provide a variety of microtube devices.
These and many other objects and advantages of the present invention, will be readily apparent to one skilled in the pertinent art from the following detailed description of a preferred embodiment of the invention and the related drawings.